2741. Seasonal Influenza Vaccine Timing in Children and Adults Hospitalized with Influenza in the United States, FluSurv-NET, 2013–2017

Abstract Background Seasonal influenza vaccine may attenuate disease severity among people infected with influenza despite vaccination, but vaccine effectiveness may decrease with increasing time between vaccination and infection. Patient characteristics may play a role in the timing of vaccine receipt. Methods We used data from the Influenza Hospitalization Surveillance Network (FluSurv-NET) and included patients ≥ 9 years hospitalized with laboratory-confirmed influenza during October 1–April 30 of influenza seasons 2013–2014 through 2016–2017 who received seasonal influenza vaccine ≥ 14 days prior to admission. Vaccine history was obtained from vaccine registries, medical charts, and patient interviews. We defined “early vaccination” as vaccine receipt before October 15 and “late vaccination” as receipt after (date selected using typical season onset and median vaccination dates). Early and late groups were compared using Chi-square or Fisher exact tests. Results Among 21,751 vaccinated patients, 61% received vaccine before October 15, and distribution of vaccination date was similar across seasons (figure). Vaccination occurred earlier with increasing age (45% were vaccinated early among those 9–17 years but 65% in those ≥ 80 years, P < 0.01). White non-Hispanic patients were more likely to receive vaccine early compared with black non-Hispanic and Hispanic patients (63% vs. 55% and 54%; P < 0.01). Those with metabolic disorders, cardiovascular disease, kidney disease, and cancer were vaccinated earlier whereas those with HIV and liver disease were vaccinated later. Vaccine timing also varied by state (P < 0.01) but not by sex. Conclusion Among influenza-vaccinated older children and adults hospitalized with influenza, older age, white race, and certain medical conditions were associated with early receipt of influenza vaccination in unadjusted analysis. This may be due to frequent healthcare encounters and targeted public health strategies in high-risk groups. Understanding how timing of vaccine receipt varies among populations can provide insights into variables that must be controlled for in studying possible vaccine effectiveness waning and attenuation of disease among those who are infected despite vaccination. Disclosures All authors: No reported disclosures.